Conventionally, a technique related to size reduction through compression and narrowing-down through expansion of a character component table has been disclosed (see, e.g., Japanese Patent No. 3333549). A technique related to size reduction of a bi-gram character component table has been disclosed (see, e.g., Japanese Laid-Open Patent Publication No. H6-68159).
A technique has been also disclosed that equivalently realizes a high speed full text search by a concatenated character component table searching unit capable of executing sufficient narrowing-down from a given retrieval term in the case of a document consisting of phonograms of a small number of character types such as English (see, e.g., Japanese Patent No. 3497243).
Retrieval performed based on a map created by using a portion of character codes leads to extraction of a file not including target characters and including non-target characters having the portion of character codes same as those used for creating the map.